Moisture-sensing controller for a clothes dryer

Abstract

A moisture-sensing circuit for a clothes dryer separates the moisture-sensing and timing functions in a way that minimizes undesirable interaction and reduces effects of tolerances in components, temperature, and supply-voltage. Separate comparators are provided for (1) the resistance of the moisture sensor as compared with a first threshold and (2) the time since occurrence of the most recent moisture signal that exceeded the first threshold, as compared with a second threshold representing a predetermined delay.

What is claimed is: 
     
       1. A moisture-sensing control circuit for a clothes dryer in which clothes are dried by tumbling, comprising: sensor means for sensing the electrical resistance of said clothes when the clothes contact said sensor means, and for providing a wetness signal accordingly;   first comparator means, including means for providing a fixed predetermined wetness threshold, said first comparator means being for comparing (a) said wetness signal with (b) said fixed predetermined wetness threshold, and outputting a first output signal according to whether (a) or (b) is greater;   capacitor means connected to receive said first output signal, and including a capacitor connected for discharging when said first output signal indicates clothes wetness greater than said wetness threshold, and for charging gradually when said first output signal indicates wetness less than said wetness threshold;   second comparator means, including means for providing a capacitor-charge threshold, said second comparator means being for comparing (c) the charge of said capacitor means with (d) said capacitor-charge threshold, and outputting a second output signal according to whether (c) or (d) is greater.   
     
     
       2. A circuit as in claim 1 and wherein said first comparator means comprises means for adjustment of the level at which said wetness signal equals said wetness threshold. 
     
     
       3. A circuit as in claim 1 and wherein said means for providing a capacitor-charge threshold comprises means for adjustment of the level at which the charge of said capacitor means equals said capacitor-charge threshold. 
     
     
       4. A circuit as in claim 1 and wherein said means for providing a wetness threshold comprises means for providing an adjustable wetness threshold. 
     
     
       5. A circuit as in claim 1 and wherein said means for providing a capacitor-charge threshold comprises means for providing an adjustable capacitor-charge threshold.